Non-return valves for vacuum pumps

ABSTRACT

A vacuum pump non-return valve comprises a valve body that defines a through-passage having an inlet side and an outlet side. A valve seat is disposed intermediate said inlet and outlet sides of the through-passage. The valve seat is defined by an insert made of an elastomeric material. The non-return valve has a ball arranged to seat against the valve seat to prevent the passage of gaseous fluids from the outlet side to the inlet side. The ball is displaceable, in use, from valve seat by pressurised gaseous fluid in the inlet side of the through-passage to permit passage of gaseous fluid from the inlet side to the outlet side of the through-passage.

[0001] This application claims priority from U.S. patent applicationSerial No. 10/655,953 filed Sep. 5, 2003 entitled NON-RETURN VALVES FORVACUUM PUMPS, by inventors Derek Savidge, Philip North and Neil Turner.

FIELD OF THE INVENTION

[0002] The invention relates to non-return valves for vacuum pumps.

BACKGROUND OF THE INVENTION

[0003] Non-return valves, sometimes referred to as check valves, arecommonly used with vacuum pumps. A non-return valve is most often usedon the exhaust side of a dry vacuum pump and is arranged to permitgas/vapour to exhaust from the pump and prevent backflow of thegas/vapour.

[0004] A known non-return valve makes use of a ball working againstgravity. In use, the ball seats against a valve seat until such time asthe exhaust pressure is sufficient to lift the ball from the seatagainst gravity. As long as the exhaust pressure is sufficient to holdthe ball off the seat, the valve is open to permit the passage ofgas/vapour from the pump. If the exhaust pressure falls to the extent itcannot support the ball against gravity, the ball falls back against thevalve seat to prevent backflow of gas/vapour into the pump.

[0005] The valve seat of the known non-return valve is made of metal andin order to provide good gas sealing properties, the ball is either madeof elastomeric material, or comprises a metal former coated with anelastomeric material. The elastomer is required to be sufficientlycompliant to provide a good gas seal.

[0006] The known non-return valve works well, but there are problemsencountered when corrosive gases/vapours are pumped. An example of sucha gas vapour is one containing fluorine. The elastomeric compoundsnormally used in vacuum pump sealing, such as fluoroelastomers, forexample, Viton (Trade Name), are prone to attack by the fluorine contentof vacuum pump exhaust. The metal components are also attacked by thesecorrosive gases/vapours, but are typically much more resistant than theelastomeric compounds normally used.

[0007] In order to cope with pumping corrosive gases/vapours, elastomershaving an increased resistance to attack can be used. Examples ofelastomers with increased resistance to fluorine attack areperfluoroelastomers, such as Chemraz (Registered Trade Mark) and Kalrez(Registered Trade Mark). However, these materials are significantly moreexpensive than the more commonly used materials such as Viton and whilea satisfactory ball made of solid Chemraz or Kelraz can be produced,this adds enormously to the cost of producing a non-return valve.

[0008] In cases where the ball is to be made by coating a metal former,the cost problem can be reduced, but the choice of elastomers that canbe used is limited by the requirement that they must be capable ofover-moulding onto a metal former.

[0009] An object of the invention is to at least partially overcome oneor more of the above-described problems and/or provide a useful choice.

SUMMARY OF THE INVENTION

[0010] The invention provides a vacuum pump non-return valve comprisinga valve body that defines a through-passage having an inlet end and anoutlet end, an annular elastomeric insert located on the valve bodyintermediate the inlet and outlet ends and defining a valve seat and aball arranged to seat against the valve seat to prevent passage ofgaseous fluids from the outlet end to the inlet end and beingdisplaceable, in use, from the valve seat by pressurised gaseous fluidin the inlet end to permit passage of the gaseous fluid from the inletend to the outlet end.

[0011] The invention also provides a vacuum pump non-return valvecomprising a valve body that defines a through-passage having an inletend and an outlet end, a valve seat disposed intermediate said inlet andoutlet ends, and a ball, wherein said valve seat is defined by an insertmade of an elastomeric material, the ball being arranged to seat againstsaid valve seat to prevent passage of gaseous fluids from said outletend to said inlet end and being displaceable, in use, from said valveseat by pressurised gaseous fluid in said inlet end to permit passage ofsaid gaseous fluid from said inlet end to said outlet end.

[0012] Desirably, the ball is made of metal. The ball may be coated witha non-stick material to prevent sticking to the valve seat. In analternative arrangement, the ball may be made of an inert, polymericmaterial, such as PTFE. As a further alternative, the ball may be madeof a ceramic material.

[0013] The insert is preferably an O-ring. The insert may be made of afluoroelastomer, or a perfluoroelastomer.

[0014] The valve body is preferably a casting.

[0015] The invention also includes a vacuum pump non-return valve, thevalve comprising a cast body part having an inlet, an outlet and alocation for receiving an insert, an insert made of an elastomericmaterial located at the location and a ball, the insert defining a valveseat and the ball being arranged to seat on the valve seat to preventpassage of gaseous fluids from the outlet to the inlet and beingdisplaceable, in use, from the valve seat by gas pressure acting on anupstream facing side thereof to permit the gaseous fluid to pass fromthe inlet to the outlet.

[0016] The invention extends to a vacuum pump, preferably a dry vacuumpump, provided with a non-return valve as aforementioned.

[0017] The invention also includes a vacuum pump having a part defininga flowpath for gaseous fluids and a non-return valve in said flowpath,said non-return valve comprising a valve seat insert and a ball, whereinsaid valve seat insert is made of an elastomeric material and beingpositioned relative to said flowpath such that when, in use, said ballis seated on the valve seat, the flow of gaseous fluids in said flowpathis prevented and when there is a predetermined gas pressure in saidflowpath upstream of the non-return valve, the ball is moved from saidvalve seat by gas pressure so that the gaseous fluid can flow topositions of the flow path downstream of the non-return valve.

[0018] The invention also includes a vacuum pump comprising a non-returnvalve in a flowpath for gaseous fluids exhausted from the pump, thevalve comprising a valve seat insert and a ball, wherein said valve seatinsert is made of an elastomeric material and is positioned relative tosaid flowpath such that when, in use, said ball is seated on the valveseat insert, the flow of gaseous fluids in said flowpath is preventedand when there is a predetermined gas pressure in said flowpath upstreamof the ball, the ball is moved from said valve seat insert by gaspressure so that the gaseous fluid can flow in said flowpath downstreamof the ball.

[0019] The invention also includes a method of preventing backflow ofexhaust gas to a vacuum pump, said method comprising providing a valveseat consisting of an insert made of an elastomeric material in aflowpath for said exhaust gas, and providing a ball on said valve seatto prevent passage of said exhaust gas, the ball being arranged suchthat it seats against said valve seat under the influence of gravity andis displaceable against gravity by gas pressure upstream of said ballvalve.

[0020] Where the valve seat is to be exposed to gases/vapours containingaggressive media such as fluorine the elastomeric material isadvantageously selected from a compound having improved resistance tochemical attack. Examples of suitable compounds are Chemraz, Kalrez orSimriz. However, the invention is not to be taken as limited to thesecompounds and valve seats made from elastomeric materials having thedesired properties for a particular pumping environment can readily besubstituted as required.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order that the invention may be well understood, an embodimentthereof, which is given by way of example only, will now be describedwith reference to the drawings in which:

[0022]FIG. 1 is a sectioned side elevation of a non-return valve mountedto a vacuum pump; and

[0023]FIG. 2 is a view corresponding to FIG. 1 showing a modifiedversion of the non-return valve.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Referring to FIG. 1, a non-return valve 10 comprises a valve body12. The valve body is typically a hollow metal casting. The valve body12 defines a through-passage having an inlet side 14 i and an outletside 14 e. Between the inlet side 14 i and the outlet side 14 e, thereis a valve seat 16 defined by an O-ring on which is seated a ball 18.Above the valve seat 16 on the outlet side 14 e side of the non-returnvalve, there is a chamber 20 into which the ball can rise. The chamber20 is open at its outer end to permit the insertion and removal of acore during the casting process. The open end of the chamber 20 isclosed by a plate 22 that is secured to the valve body by means ofcap-head socket screws or the like. The plate 22 seals against a seal 24that is provided between the valve body 12 and the plate to provide agas-tight seal.

[0025] A flange 26 is provided at the outer end of the inlet side 14 iof the through-passage, i.e. the end that is remote from the valve seat16. The flange is provided with suitable through-holes (not shown)through which screws can pass to allow the non-return valve to besecured to a vacuum pump 28. A recess 30 is provided in the flange 26 toreceive a seal, such as an O-ring, to provide a gas-tight seal between avacuum pump 28 and the flange 26. Similarly, the outer end of the outletside 14 e of the through-passage is provided with a flange 32 and arecess 34 to permit a gas-tight connection to be made to downstreamapparatus, or a conduit leading to such apparatus. An example ofapparatus that might be connected downstream of the non-return valve isan abatement system.

[0026] At the lower, or inner end, of the chamber 20, the valve body 12defines a shoulder in which the O-ring 16 seats. The O-ring comprisesany suitable elastomeric compound. If the non-return valve is to be usedto pump aggressive fluorine containing gases/vapours, the O-ring shouldbe made of a suitably resistant compound, such as Chemraz or Kalrez.

[0027] The ball may be made from a metal, such as a stainless steel orother suitable metal, which will usually be selected for its resistanceto corrosion. However, a metal ball will require a certain amount ofpressure to be built up behind it before moving and thus activating thevalve. In a further embodiment an inert polymeric material such as solidpolytetrafluoroethylene (PTFE) may be used to form the ball. A ballformed from such a material will be significantly lighter than theequivalent metal ball such that the pressure required to lift the ballis reduced. In this way a valve is provided that is more sensitive topressure fluctuations and, consequently, the magnitude of the backpressure seen by the pump exhaust will be reduced. Further advantagesare provided by such an approach in that a polymeric ball will not onlybe lighter but will be cheaper and easier to manufacture and in use willresult in a significantly quieter device.

[0028] As an alternative, ceramic may be used to form the ball.

[0029] In use, when the pump 28 is pumping, exhaust gases pass from thepump into the inlet side 14 i of the through-passage and provided thereis sufficient pressure, the ball 18 is lifted from the O-ring thatdefines the valve seat 16, permitting the passage of the exhaust gasesinto the lower end of the chamber 20 and from there into the outlet side14 e of the through passage, from where the gases pass from thenon-return valve. If the pressure from the pump 28 falls to the extentit is insufficient to support the ball 18, the ball falls back againstthe valve seat 16 under the influence of gravity. When the ball 18 seatsagainst the valve seat 16 defined by the O-ring, a substantiallygas-tight seal is provided between the sides 14 i, 14 e of thethrough-passage, thereby preventing the backflow of gases into the pump28.

[0030] It will be appreciated that the valve body 12 may take manyforms. For example, it is not essential to provide the outlet side 14 eof the through-passage as shown. Instead, the chamber 20 could definethe outlet end of the through-passage, by removing the plate 22. In suchan arrangement, there would typically be a flange similar to the flanges26, 32, provided in the region occupied by the plate 22 in FIG. 1.

[0031] It will be appreciated that where expensive compounds such asChemraz or Kalrez are to be used, the non-return valve 10 has advantagesover the known valve provided with a solid elastomeric ball. Asindicated previously, compounds such as Chemraz and Kalrez are expensiveand it is estimated that a valve seat 16 in the form of an O-ring madefrom such materials will cost in the region of 7% of the cost of a solidball made from the same material.

[0032] A further advantage of the non-return valve shown in FIG. 1, ascompared with a valve using a ball comprising a metal former coated witha compound, is that it is not limited to using compounds that arecapable of being moulded onto a metal former. Thus, in terms ofselecting a suitable compound for a particular operating environment,the freedom of the designer is enhanced.

[0033] Furthermore, because the designer is not so much constrained bycost of the compound or the need for the compound to be capable ofmoulding onto a former, when new elastomers having improved qualitiesbecome available, it is relatively straightforward to bring them intouse in the non-return valve.

[0034] It is to be understood that while the valve seat 16 isconveniently defined by an O-ring as shown in FIG. 1, the valve seat canbe defined by insert seals having a different configuration, should thisbe required and/or desirable.

[0035] It will be appreciated that the ball while made of metals may becoated with a non-stick material to prevent it from sticking to thevalve seat 16. An example of a suitable non-stick material ispolytrifluorochloroethylene (PTFE).

[0036] It will be understood that whilst the embodiment is described ashaving flanges, which allow the non-return valve to be secured to avacuum pump and piping leading from the vacuum pump by means of screwsor the like, this is not to be taken as limiting. For example, the valvebody could be provided with threading so that the valve could be screweddirectly to cooperating threading on a vacuum pump.

[0037] It will also be appreciated that the non-return valve may beprovided by fitting the insert valve seat 16 and ball 18 into a passagedefined in a pump and in this case, the pump, or a part of the pump,will define the valve body 12.

[0038] A possible modification to the non-return valve 10 is shown inFIG. 2. The modification comprises the provision of a compression spring40 between the ball 18 and the plate 22. The spring 40 is arranged tobias the ball to a position in which it engages the valve seat 16defined by the O-ring. It will be appreciated that spring can beselected such that the ball will not lift from the valve seat until thepressure of the gas/vapour in the inlet side 14 i of the through-passageat least reaches a predetermined threshold and the presence of thespring will ensure that if the pressure in the inlet side falls belowthat threshold pressure, the ball will promptly be pressed back againstthe valve seat to prevent the backflow of gas/vapour from the outletside 14 e to the inlet side 14 i.

[0039] In summary, a vacuum pump non-return valve comprises a valve body(12) that defines a through-passage having an inlet side (14 i) and anoutlet side (14 e). A valve seat (16) is disposed intermediate saidinlet and outlet sides of the through-passage. The valve seat (16) isdefined by an insert made of an elastomeric material. The non-returnvalve has a ball (18) arranged to seat against the valve seat to preventthe passage of gaseous fluids from the outlet side (14 e) to the inletside (14 i). The ball is displaceable, in use, from the valve seat bypressurised gaseous fluid in the inlet side of the through-passage topermit passage of gaseous fluid from the inlet side to the outlet sideof the through-passage.

[0040] While the foregoing description and drawings represent thepreferred embodiments of the present invention, it will be apparent tothose skilled in the art that various changes and modifications may bemade therein without departing from the true spirit and scope of thepresent invention.

1. A vacuum pump non-return valve comprising a valve body that defines athrough-passage having an inlet end and an outlet end, an annularelastomeric insert located on the valve body intermediate the inlet andoutlet ends and defining a valve seat, and a ball arranged to seatagainst the valve seat to prevent passage of gaseous fluids from theoutlet end to the inlet end and being displaceable, in use, from thevalve seat by pressurised gaseous fluid in the inlet end to permitpassage of the gaseous fluid from the inlet end to the outlet end.
 2. Avacuum pump non-return valve comprising a valve body that defines athrough-passage having an inlet end and an outlet end, a valve seatdisposed intermediate said inlet and outlet ends, and a ball, whereinsaid valve seat is defined by an insert made of an elastomeric material,the ball being arranged to seat against said valve seat to preventpassage of gaseous fluids from said outlet end to said inlet end andbeing displaceable, in use, from said valve seat by pressurised gaseousfluid in said inlet end to permit passage of said gaseous fluid fromsaid inlet end to said outlet end.
 3. A valve as claimed in claim 1wherein said ball is made of a material selected from the groupcomprising metal, polymer and ceramic.
 4. A valve as claimed in claim 3wherein said ball is coated with a non-stick material to preventsticking to said valve seat.
 5. A valve as claimed in claim 1 whereinsaid insert is an O-ring.
 6. A valve as claimed in claim 1 wherein saidinsert is made of a material selected from the group comprisingfluoroelastomer and perfluoroelastomer.
 7. A valve as claimed in claim 1wherein said valve body is a casting.
 8. A vacuum pump non-return valvecomprising a cast body part having an inlet, an outlet and a locationfor receiving an insert, an insert made of an elastomeric materiallocated at the location and a ball, the insert defining a valve seat,the ball being arranged to seat on the valve seat to prevent passage ofgaseous fluids from the outlet to the inlet and being displaceable, inuse, from the valve seat by gas pressure acting on an upstream facingside thereof to permit the gaseous fluid to pass from the inlet to theoutlet.
 9. A vacuum pump comprising a non-return valve in a flowpath forgaseous fluids exhausted from the pump, the valve comprising a valveseat insert and a ball, characterised in that said valve seat insert ismade of an elastomeric material and is positioned relative to saidflowpath such that when, in use, said ball is seated on the valve seatinsert, the flow of gaseous fluids in said flowpath is prevented andwhen there is a predetermined gas pressure in said flowpath upstream ofthe ball, the ball is moved from said valve seat insert by gas pressureso that the gaseous fluid can flow in said flowpath downstream of theball.
 10. A pump according to claim 9 wherein the insert comprises anannular elastomeric insert located intermediate an inlet end and anoutlet end of the flowpath.
 11. A method of preventing backflow ofexhaust gas to a vacuum pump comprising providing a valve seatcomprising of an insert made of an elastomeric material in a flowpathfor said exhaust gas, and providing a ball on said valve seat to preventpassage of said exhaust gas, the ball being arranged such that it seatsagainst said valve seat under the influence of gravity and isdisplaceable against gravity by gas pressure upstream of said ball.